1. Field of the Invention
The present invention relates to a method for measuring a refractive index and a thickness of a thin film and an apparatus therefor.
2. Description of the Related Art
There are many semiconductor devices and optical devices in which a thin film is formed. It is important to accurately measure a refractive index of the thin film, a film thickness, etc. with respect to performance of these devices.
In an ellipsometry known as a method for accurately measuring the refractive index and thickness of the thin film, a complicated large-sized device is required when the refractive index and thickness of the thin film are measured. For example, in Japanese Patent Application Laying Open (KOKAI) No. 2-75985, the inventors of this application proposed a series of measuring methods instead of the ellipsometry.
In such general measuring methods, monochromatic light is basically irradiated onto a thin film formed on a substrate to measure a reflectance of each of S-polarized light and P-polarized light. The refractive index of the thin film is calculated by numerically solving a predetermined equation based on the measured reflectance of each of the S-polarized light and the P-polarized light. An arc cosine function is included in this equation used in a numerical calculation. This arc cosine function is greatly changed with respect to a change in refractive index of the thin film as a measured object so that the calculation must be made with very high accuracy in a certain case. Further, only the refractive index of an uppermost layer is measured when the thin film is composed of a plurality of layers.